This invention relates to a system for protecting boat""s electrical systems and personnel, and prevents degradation to both noble and sacrificial elements on the boat due to both Alternating Current (AC) and external Direct Current (DC) electrical effects. It also protects other boats and personnel at the marina from electrical problems arising within the protected boat. In all of these cases, protection is provided against potentially lethal electric shock to personnel, as well as uncontrolled currents in the marina, boat, and surrounding water that contribute to severe electrolytic corrosion, or externally induced galvanic action.
It is normal practice to provide power sources for boats at marinas, which commonly is a 3 or 4 wire AC system for the electrical devices on the boat, including battery charger, lights and other auxiliary devices.
It is also common practice to provide protection for the hull, conductive fittings, paint, and other conductors in and on the boat against corrosion that is commonly called DC galvanic action, which arises, for example, when a metal boat and a dissimilar metal such as the propeller are both in the aqueous, particularly salt seawater solution.
However, problems have arisen concerning these AC and DC boat systems. In many cases the AC power source at the marina is not properly wired and may have power, neutral, and safety ground lines interchanged (commonly called reversed polarity). In many cases the AC system on the boat is not properly wired, or has AC leakage to the boat ground. These problems cause leakage or fault AC currents, which can be life threatening to boat and marina personnel, and cause serious harm or failure to underwater parts and electrical devices on the boat.
The DC systems provided to overcome the galvanic action provided on the boat are frequently interconnected with the AC safety ground. Leakage currents through this path result in accelerated corrosion. AC voltage on the AC safety ground represents a serious electrolysis and safety problem for all boats, marina apparatus and personnel.
These effects cause four types of damage:
First, this interconnect causes all underwater protective active elements (typically zinc""s) and the more noble underwater metallic parts of all the boats with a DC ground connected to the AC safety ground wiring in the entire harbor to be hooked together electrically. The result is a very large area electrolytic corrosion network, making the entire harbor into a much larger wide-spread area battery which may rapidly deplete the more active elements. This is caused by the combined effect of galvanic corrosion from all boats.
A second form of damage is electrolytic corrosion caused by introducing harbor AC electrical power commonly connected into the DC ground systems of boats. This arises due to improper wiring, leakage, and AC return line voltage drop that is inducing low levels of AC voltage into the common AC shore power safety ground. This can result in depletion of both the active elements, and the more noble underwater elements of a boat. This type of damage is particularly insidious, because it attacks all through hull fittings, corroding and eventually destroying them, so the boat can easily be subjected to flooding due to failure of the through hull fittings. This phenomenon has reportedly caused unprotected or unmanned boats to sink at the dock. Even wet, normally non-conductive underwater material, like wooden hulls, have been reported to be damaged by this action. It is also a common problem in destroying conductive surfaces including copper based bottom paint. This effect can be visually identified after it has occurred by large numbers of small xe2x80x9cpock marksxe2x80x9d in the paint when the boat is hauled out of the water.
A third failure mechanism is electrical damage that develops as a result of leakage current unbalance in shore electric power delivered to the boat. This happens when current is being supplied to the boat, but not returning through the intended return line. The unbalanced current can be leaking off through the water into the marina, or through the AC safety ground. This type of fault has reportedly killed persons by electrocution that were swimming, were in or on, or went into the water near a boat with this type of failure. As little as 15 Milliamperes (ma) is considered the safe level of current that a human body can withstand. This type of failure in an otherwise properly wired boat may be caused by movement of electrical contacts touching each other in an electrical distribution panel, or by sea water invading a circuit that is intended to be insulated, but leaks off to ground through the wet area. Some electrical systems, like refrigerators, heaters, air-conditioners, or timer run devices may have faults that do not activate until switched on unexpectedly, long after the operators have departed the boat.
A fourth common damage prevention deficiency is the ability to test, isolate both AC and DC faults and leakage, and document deterioration trends. This can provide identification of a potential problem""s existence and point of origin prior to extensive or irrecoverable damage, particularly desirable with the boat in continued operational use.
U.S. Pat. No. 3,362,900 discloses a cathodic protection system in which a transformer 20 together with transistors 48, 50 provide cathodic protection from the boat 110 vac. This is an active DC protection system for balancing out any galvanic current damage to the hull of the protected boat. It is intended to solve the boat""s self generated electrolysis effect. However in this system there is no protection for the boat or personnel from AC currents, which may be faulty from the marina power source. The Electrical Test/Isolator (T/I) described herein makes no claim for protection against this type of problem, only against externally induced, or electric fault destructive effects.
U.S. Pat. No. 3,636,409 also utilizes a transformer 2 and a filter system 11 is connected to the boat ground 9. As shown in FIG. 2 the protective system includes a first pair of rectifiers 12 and 13 in series with each other and the second pair of rectifiers 14 and 15 in series with each other and of opposite polarity to rectifiers 14 and 15. Capacitors 16, 17 are in series with each and in parallel with the rectifiers. However this system does not provide protection against faulty AC marina supply systems.
U.S. Pat. No. 3,769,926 is somewhat similar. In FIG. 2 this patent discloses a protective system including opposite polarity diodes 36a, 36b, and 38a, 38b connected in parallel with each other. It is noted that this system does not include the capacitors as were provided in the previous reference system. However this patent provides no protection against faulty AC marina supply sources.
U.S. Pat. No. 4,117,345 includes a ground isolator circuit which monitors the DC provided for galvanic protection, and also monitors the AC circuit between the boat ground connection and the ground connection at the dock. The reference points out that any voltage above about 2.5 volts RMS could conceivably be dangerous when contacted by a person in the water. This system provides protection against DC voltage and thereby prevents externally induced corrosion of the hull of vessels due to electrolysis. It also limits the AC potential between the hull and the shore ground to a level safe for humans, at the stated 2.5 volts RMS potential value. However this reference does not provide corrosion protection below the stated level, or against the AC marina supply system that is faulty for reasons other than externally induced stated levels of the boat to dock ground connection. Further, this is a relatively complicated system with many circuits, parts, and expensive electrical components, resulting in decreased reliability and increased cost. Furthermore the system requires continuous AC or DC power to function properly. Furthermore if the system detects an unsafe level, the system only sounds an alarm, which is typically unmanned on recreational vessels at dock, and does not disconnect the unsafe system.
U.S. Pat. No. 5,627,414 discloses an automatic Marine Cathodic Protection System utilizing galvanic anodes to provide protection against self induced galvanic corrosion. It is primarily an active cancellation system installed internal to the vessel. It appears intended for use on fully staffed large commercial vessels, as opposed to small recreational vessels, where the primary corrosion and safety concerns, and staff availability are different. Commercial vessels are primarily concerned with minimizing self induced corrosion over dispersed, not easily replaced galvanic elements on the vessel itself, primarily at sea, while a primary problem on small recreational boats is prevention of external corrosion effects while in port. An incidental reference to a protective circuit that contains some similar elements to the T/I proposed herein is described on page 8 paragraph 45 through the fourth paragraph of column 9 and referenced in FIG. 5. However, as stated in that claim the purpose is to protect against incidental external DC galvanic action currents. That claim differs from the proposed T/I in that it does not include a GFCI that would provide unbalanced current protection. Further, that claim includes a fuse in the ground line, allowing the possibility of not protecting by the safety ground, while also not indicating low level difficulties due to the large level of voltage anticipated for the major fault indicator identified as 168. Further, It claims to only provide an indicator, or alarm for external stray currents (although not identified in detailed mechanization) and does not protect against those stray currents. The diode string is clearly stated in column 8, paragraph 60, as protection against (apparently plus or minus) DC galvanic current only, which is stated to never exceed 2 volts. The T/I proposed is specifically intended to protect against AC ground voltage presence problems which are well in excess of these levels, as well as the identified DC ground currents. Typical Marina AC ground voltage problem levels may be well in excess of 3 volts peak. This is primarily due to the increasing number offending recreational boats plugged in at marinas. It is specifically noted that the device is a complex electromechanical mechanization with many components, therefore being subject to relatively poor Mean Time Between Failure (MTBF) performance due to large parts count and failure prone moving parts. It is specifically noted that the T/I proposed herein is a simple, reliable device that makes no claim to provide active cancellation. Further, the T/I proposed herein is compatible with shore power operation with U.S. Pat. No. 5,627,414 utilization to provide further performance improvement of that device.
U.S. Pat. No. 5,574,610 specifically claims to allow (AC) fault currents or lightning surge currents to pass freely. Unlike that device, the T/I device herein proposed specifically protects against such faults by disconnecting the AC power, and isolating the low-level voltage. Further, U.S. Pat. No. 5,574,610 discloses a series of stacked diode circuits in each identified configuration, each containing a capacitor used to by-pass AC current into the safety ground system. Unlike that device, the T/I device herein proposed does not include a capacitor, nor propose to allow either AC or DC ground faults to continue unabated, since either can be very destructive. Further, U.S. Pat. No. 5,574,610 column 7 specifically claims to introduce a cathodic DC protection voltage. Unlike that device, the T/I device herein proposed claims no actively introduced galvanic voltages, but rather seeks to passively isolate the offending voltages introduced, even to considerably higher voltage levels that also include AC, the primary offending culprit.
U.S. Pat. No. 5,840,164 provides a system for protecting against galvanic corrosion by providing circuits between the boat ground and the shore ground, each containing a capacitor to by-pass AC safety ground currents. This suffers from the AC limitations identified in other patent reviews above. The reference does not disclose protecting the boat and personnel against faulty marina AC supply sources. Further, U.S. Pat. No. 5,840,164 proposes a high heat dissipation device, requiring protective circuits of relays and thermostats to alleviate the heat load, while allowing damaging corrosion currents to continue destructive action. Unlike that device, the T/I device herein proposed passively seeks to isolate the offending currents with a low heat dissipation implementation. For example, even at the highest level of 1.4 volts quoted in U.S. Pat. No. 5,840,164, the heat dissipated in the proposed T/I device is at the insignificant level of approximately 0.00003 watts. Heat is a major contributor to typical failure mechanisms of any device, particularly solid state devices, thus potentially rendering any device, independent of it""s intent or merit, to fail to accomplish it""s intended purpose.
U.S. Pat. No. 5,748,008 discloses an electrical integrity test system for boats which provides circuitry for evaluating the integrity of the boat""s electrical AC grounding system when the boat is connected to a dock electrical distribution system and the integrity of the boat""s galvanic isolator system. If a problem is found the circuitry will activate an alarm to appraise the boat operator of the faulty condition. However it does not disconnect the power and merely sets off an alarm if a problem is detected. Furthermore the system requires continuous AC or DC power to function properly. Furthermore, it is a very complicated system with many circuits, parts, and expensive electrical components, resulting in decreased reliability and increased cost.
The foregoing prior art references are hereby incorporated into the present application by this reference as if fully set forth herein.
One object of the present invention is to provide a device and method to determine whether or not a boat and marina""s AC and DC circuitry condition is safe for the boat to be connected to a marina""s electrical system.
Another object of the present invention is to provide protection against externally induced AC electrolytic corrosion of parts on the boat.
Another object of the present invention is to provide protection of parts of other boats and equipment in a marina against AC and DC induced electrolytic or galvanic corrosion due to the protected boat being connected to the marina.
Another object of the present invention is to provide protection against faulty electrical currents in the marina electrical supply system, which can cause harm to boat equipment.
Another object of the present invention is to provide protection against AC current unbalance faults, which can harm personnel on the boat, in the water or near the marina.
Another object of the present invention is to provide circuitry to allow isolation and testing of the magnitude of any electrical problems with the marina""s electrical system, including other boats connected to the Marina electrical supply.
Another object of the present invention is to reduce or eliminate electrocution of personnel, which has caused death and injury to persons in and around marinas.
Another object of the present invention is to reduce or eliminate externally induced electrolytic DC corrosion, commonly called galvanic action.
Another object of the present invention is to reduce or avoid destruction of boats including through hull fittings.
Another object of the present invention is to reduce or avoid the number of boats being sunk.
In accordance with the present invention, a method and apparatus including a ground fault current interrupter is provided to test both the marina""s AC power, and the boat electrical system, to make sure that both are of the proper wiring configuration and safe to be connected. A low voltage high impedance current path including a multiplicity of diodes in series to protect against inadvertent low level AC supplied through the marina, and DC current due to the harbor safety ground interconnect between boats in the harbor is also provided. The low voltage high impedance ground current path includes an oppositely connected pair of a series of silicon diodes, in number sufficient to raise the voltage to a safe level encompassing the typical combined AC and DC ground fault in a Marina. Due to increasing numbers of faulty boats and Marinas, that level is sometimes in excess of 2.5 volts. While many non-linear devices could function in this role, at least four series silicon diodes in each of the pairs can be used. Silicon diodes are inexpensive, available, have high surge current tolerance, and are reliable in this application. This configuration protects against low level AC ground faults present in the marina, as well as DC current due to the harbor safety ground interconnect between boats in the harbor. Test points are provided to determine the current that would be flowing through the safety ground had the protection not been installed. The same two test points provide for measurement of the voltage across the diodes without disconnect or movement of the test leads. A calibration is provided whereby the resulting residual current may be determined from the measured voltage.
The marina power to the boat is automatically disconnected and a fault indicated if the AC current supplied to the boat exceeds a predetermined amount of unbalance between the high (hot) and return (neutral, or common) lines due to leakage into either the water or the safety ground line.
In accordance with the present invention, a method and apparatus including tests conducted from the T/I, supplemented by the test devices identified herein, and utilizing the attached Test Procedures, (identified as xe2x80x9cSafety Operating Manual for the Electrical Test Isolatorxe2x80x9d copyright Donald G. Funderburk 2001 attached hereto is hereby incorporated into the present application by this reference as if fully set forth herein. This periodic testing method and apparatus includes an AC xe2x80x9cCircuit Testerxe2x80x9d provided to initially and periodically test for proper AC power and wiring at the marina AC service connectors. This periodic testing method and apparatuus also includes a xe2x80x9cGround Fault Simulation Testerxe2x80x9d (GFST) validation device provided to initially and periodically test for complete safety ground operation and protection.